CMOS vs CCD

Discussion in 'Beyond the Basics' started by photong, Apr 8, 2005.

  1. photong

    photong Typo Queen

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    I tried searching lastnight for it and I couldn't find anything.

    I know I did an assignment in college and it looked like CCD was better than the CMOS. But I forget why. I think it was a sharper image? I'm not sure.

    If anyone could point me int he right dorection through yourself, a thread or website, thank you. I don't have time to search on google and I need to know so maybe I can buy a new camera this weekend :D Weeeeee..
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    You might as well compare Ford to Chevy...Coke to Pepsi...etc.

    There are so many factors that go into image sharpness that buying a camera based upon the type of sensor seems silly. IMO
     
  3. ferny

    ferny TPF Noob!

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    I've not read this, haven't got time. It's from the Konica Minolta Photo World site. I remember seeing it when I first joined.







    Light sensors in digital cameras – light becomes an electrical current


    As is common knowledge, a light sensor takes the role of traditional film material in digital cameras. It converts the incident light into electrical signals, thus generating an image signal.

    With development of high-resolution sensors, a new era of image recording technology has been heralded, and the traditional film-based image recording procedures are starting to pale by comparison

    In this article, we want to focus on the basic mode of operation of the light sensor and introduce two different types of sensors.

    [​IMG]


    CCD and CMOS – What's the difference?

    Same physics – different composition

    In both technologies, the photo-diodes are the key element of the light-sensor. They are responsible for converting incident light into an electrical signal.

    Here CCD and CMOS principally work exactly the same way and both are based on the so-called photoelectric effect. To make the functionality clear, we have to briefly branch off into semiconductor technology, because the basic material of all sensors is the semiconductor silcon.
    [​IMG]



    Semiconductors


    Semiconductors are materials whose conductivity is located between highly conductive elements and isolators.

    To selectively affect the conductivity of semiconductors, impurities are added – they are endowed. When endowing, foreign atoms are inserted into a rigid crystal-structure. So-called n-(negative) and p-(positive) semiconductors are the result.




    If a p- and a n-semiconductor are adjoined, a thin border-layer with an ideal crystal-structure is created; the distinct halves are now respectively charged positively and negatively. If light lands on the n-layer, it can penetrate it, until an electron is knocked out of the border-layer.

    If the p- and n-layer are now combined, a current of electrons arises: light has become electricity!
    [​IMG][​IMG]



    Differences CCD/CMOS


    While CCD and CMOS-sensors are based on the same effect, they differ fundamentally in the way the image data is read out from the chip.

    The word CMOS (Complementary Metal Oxide Semiconductor – transistors, that are arranced in pairs complementary to each other) refers to the way the sensors are produced.

    By contrast to the CCD (Charged Coupled Device), where the current that is generated by each photo-diode is read out, transported (bucket brigade principle) and finally amplified and digitized on a line by line basis, the amplification and digitalization in a CMOS is done for every pixel directly by individually dedicated control-elements on the same chip that contains the light-sensitive photo-diodes.
    [​IMG]
    [​IMG]



    What counts in practice?


    The majority of up-to-date digital cameras work with CCD-sensors; it's only recently that CMOS sensors have also been used.

    Since CMOS-sensors consist of the same material as common computer components and the control- and processing-elements are, unlike the CCD-sensor, integrated into the sensor in a single production process, CMOS-technology is more cost-effective.

    This advantage is, however, relatively small for digital cameras.

    While numerous low-cost devices like webcams work using CMOS-sensors, the costs for production rise proportionally to the demands on image quality, due to the necessarily complex image-signal enhancing, so that in the end both technologies are roughly equally expensive for high-quality applications.

    Without elaborate image-signal enhancing, the CMOS-technique suffers from heavy image-quality problems, especially from image noise, and the multitude of integrated control-circuits results in a lower light-sensitivity (owing to the small size of a photo-diode).
    [​IMG]


    CMOS – advantages at the moment mainly in beginner applications


    For the time being, CMOS-technology can trade off its advantages mainly in those fields where a small size (for example mobile-phones with camera) and a cost-efficient mass-production are mandatory. The energy-consumption can, due to the sensor-composition, also be held to a very low level in such devices.

    The possibility of individually addressing each pixel in a CMOS-sensor plays no decisive role in current camera-technology and is of greater interest in special appable technology and can list advantages with respect to the most important image-quality criteria like light-sensitivity, signal-to-noise ratio and dynamic range in the most applicatilications like mechanical image analysis.

    If the image quality is the top-priority, CMOS technology loses, for the time being, its advantages over the CCD, and CMOS high-end cameras are neither cheaper, nor consume significantly less energy than comparable cameras with CCDs.

    CCD – standard for high-developed image recording technology


    If the image quality is the top-priority, CMOS technology loses, for the time being, its advantages over the CCD, and CMOS high-end cameras are neither cheaper, nor consume significantly less energy than comparable cameras with CCDs.

    CCD – standard for high-developed image recording technology

    CCD-technology is a highly-developed and relion classes.

    The future: CCD or CMOS?


    Both systems have their specific strengths and weaknesses, but it is unlikely that one technology will 'prevail' over the other. It is far more likely, that future sensor-systems will try to combine the advantages of both systems; which is spoken of as hybrid sensor technology.
     
  4. Meysha

    Meysha still being picky Vicky

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    That's funny. Because I read in a photography magazine a few years ago that the CMOS chips were better than the CCD. Unfortunately I can't remember much of the article.
    It showed 2 photos of the same thing but each taken with different sensors but all the other settings were the same. It was a picture of tree leaves againts a bright blue sky. And the CMOS sensor won by a huge margin. The detail around the leaves was by far better. With the CCD sensor there was noise and the shape of the leaves was a bit distorted and wasn't as sharp.
     
  5. photong

    photong Typo Queen

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    Wow....i really don't know anymore...in college, the CCD won and it was obvious too when comparing. I wish I wasn't lazy to go find those pictures. I'm sure theyre somewhere :(

    I ask because I was looking into the Canon Rebel (http://www.blackphotostore.com/english/proddetail.asp?sku=4295) :( Now I know why it's only 1k Canadian :( That CMOS sensor and it's small I think, and prolly made out of plastic. Not that the two later things mater, it's the image quality and clour I care about.

    Thank you everyone, especially Ferny :D
     
  6. ferny

    ferny TPF Noob!

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    I (used to) post on a digital only forum and everyone seemed happy with their Rebel's. As far as I know Canon are the only people who use CMOS sensors but I don't think it makes all that much difference. Cameras from large companies and in the same price bracket normaly perform around the same. The Rebel has a very good reputation, or did when I last heard. I think the price is more down to it being a couple of years old, not it's quality.

    Here's a review of the Rebel.
     
  7. ferny

    ferny TPF Noob!

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  8. Unimaxium

    Unimaxium TPF Noob!

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    I think that article ferny posted could be a little biased, considering that it is from konica-minolta, who uses CCDs. Essentially it seems that they say CMOS is better in camera phones and webcams while CCD is better in higher-quality cameras. Kinda sounds like they're trying to put Canon down here.
     
  9. DocFrankenstein

    DocFrankenstein Clinically Insane?

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    That article is at least 5 years old. The technology has changed significantly since then.

    For starters, control elements of the CMOS are no longer on the surface, so the diodes can get all the lights they need.

    Moreover, Canon's new CMOS sensors now have a microlense over each pixel, thus gathering more light than they did before from the corners of the pixel.

    On a picture with cups, imagine that every cup has a rectuangular funnel above it.

    20D, XT and 1Ds MkII have these microlenses, not sure about other ones.
     
  10. DocFrankenstein

    DocFrankenstein Clinically Insane?

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    Ok, first one is crap. copyright 2000 :er:

    Second one is... closer, but still outdated.

    Dalsa is pure crap also. As I said above, the fill factor for CMOS right now is better than the CCD.

    The bottom line is that the best DSLRs of today are using the CMOS with great results. I have the Digi Rebel with CMOS and I am more than happy with the image quality. Canon CMOS sensors also handle high ISO settings way better than any other DSLRs out there.

    Besides being old and outdates, those reviews are crap because they're equal to my saying "CMOS is way cooler than CCD, yo!"

    If you want to compare the 2 of them, you set up an experiment and measure the noise levels in dB at different ISO settings for every channel... and compare the color response curves or something.

    Then you'd be able to say that one is better than the other.

    Otherwise, all those artices are internet garbage. Take a look at the image samples for the cameras at DP review. 300D has useable ISO to about 400. Rebel XT seems to be useable at 1600

    Cheers
     
  11. Hertz van Rental

    Hertz van Rental TPF Noob!

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    Oh God! It's the digital equivalent of the 'which film is best' argument. Can you all remember to put on your anoraks so we can avoid you?
     
  12. Unimaxium

    Unimaxium TPF Noob!

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    Well, this can be either a "which film is best" - style discussuion, or we could always turn this into a Canon vs. Nikon argument. They're always fun :lol:
     

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